Chicken and Pea Salad

• 1 cup frozen peas
• 4 cup lettuce, roughly chopped
• 1.5 cup cooked chicken pieces
• 0.25 red onion, thinly sliced
• 1 avocado, thinly sliced
• 30 ml white vinegar
• 30 ml vegetable oil
• 1 garlic clove, crushed
• 0.5 tsp black pepper
• 0.5 tsp salt